Pulse repeater



J. R. PIERCE PULSE REPEATER Feb. 21, 1956 I5 Sheets-Sheet 1 Filed Sept.9, 1950 Q Grt um TZ mmh dfi Vv@ /NN \N @Mk il A T TORNE V Feb. 21, 1956Filed Sept.

J. R. PIERCE PULSE REPEATER 3 Sheets-Sheet 2 T/ME /NVENTOR R. P/ERCE#www 4 A "T Tom/Ey J. R. PIERCE PULSE REPEATER Feb. 21, 1956 Filed Sept.9, 1950 I5 Sheets-Sheet 3 /A/l//E/VTOAJ By J. R. P/E RCE ATTORNEV UnitedStates Patent 2,735,933 l PULSE REPEATER Jolin R..Pierce, BerkeleyHeights, N. J., assigner to Beil Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application september 9,1950, serial No. matas 1sV claims. (ci. 25o-1s) system where repeaterspacing is relatively small, for example, onthe order of a few miles. Arelated object of the invention is ,a pulse repeater which is simple ofdesign and which is sufficiently inexpensive to warrant close repeaterspacing.

,Another object of the invention is to relay extremely sliort pulses atmicrowave frequencies and to partially reshapeA and retime the pulsesbeing relayed.

further object of the invention is to amplify, reshape and retimemicrowave pulses without reducing the pulses to anin'termediatefrequency.

A more specific object of the invention is a relatively inexpensive,incompletely regenerative pulse repeater for use ina radio relay systemat wavelengths on the order of one and one-half centimeters or less andwhich is capable of handling over a thousand broad-band channelsmultiplexed in time division.

Another object of the invention is to regenerate a broad-band radiofrequency signal consisting of very short pulses without requiringbroad-band auxiliary amplifiers. A great portion of the initial cost andcarrying charges of a. microwave .pulse communication system of theradio relay ltype lies inthe repeater stations. In present known systemsthe cost per mile is reduced by keeping the spacing between repeaters aslarge as possible, for example, 0n the order of from 35 to 50 miles.This, however, requires that the wavelength be kept greater than about 5centimeters to avoid excessive rain attenuation; longer wavelengths inturn require `larger antennas. Greater antenna spacings also requireobstruction clearance locations for the repeaters due to the line ofsight nature of microwave propagation. This means either very tall andexpensive towers or hilltop sites` which require both expensive siteacquisition and expensive road construction and maintenance.

It may therefore be seen that if the cost of the repeater stations canbe made low enough to permit closer spacings several advantages willresult. For example, shorter wavelengths may be used in spite of rainattenuation since this type of attenuation is proportional to distance.Also, with shorter sp'acings and wavelengths, antennas may be smallerand obstruction clearances may be less, even over flat terrain. Further,roadside repeater sites and smaller and lessexpensive tower structuresbecome permissible.

lComplete regeneration, that is, accurate reshaping and reti'rning ofthe transmitted pulses, has been proposed in the' past. However, in aradio relay system itis unlikely that deep fading will occursimultaneously on any two adjacent links. VThe present inventiontherefore makes use f 'a repeater which is incompletely regenerativemakigit extremely simple of design and hence relatively inexpensive. Inan illustrative repeater embodying prineipls of the invention anddescribed below in detail the 2,735,933 Fatented Feb. 2l, 1956 receivedpulses are partially reshaped by an expander which discriminates infavor of the higher amplitudes tending to reduce the lower noise signalsto zero and by a limiter which establishes the peak pulse amplitude.Partial retiming is effected by a variable gain device whose gain iscontrolled by a sinusoidally varying voltage of the pulse repetitionfrequency which is derived from the incoming pulse train and which is sophased as to give the repeater maximum gain only at the center of eachnominall pulse occurrence time. In completely regenerative repeaters ofthe type disclosed in a copending joint application of R. L. Carbrey, C.C. Cutler and C. B. H. Feldman, Serial No. 176,238, led July 27, 1950,which issued as Patent 2,658,997, dated November l0, 1953, incomingpulses are recirculated through a loop circuit containing reshapingelements to completely reshape and accurately retime the pulses beforetransmitting them to the next station. In accordance with the presentinvention distorted pulses are only partially reshaped and rettned ateach repeater. On the original premise that deep fades will not occurbetween adjacent repeaters, the pulses wiil have an opportunity to tendto become completely reshaped and retimed by passing through severalsuccessive repeaters without encountering appreciable noise or fading.

Means to change the carrier frequency at the repeaters are omitted tokeep the repeaters as simple and economical as possible. ifgeographicalconditions do not protect against overshoot, that is, if a signalemitted by one repeat-er may be picked up not only by the subsequentrepeater but also by other down the line the route may be laid out in azig-zag manner, the angle of deviation being primarily a function of theradiation pattern of the antenna.

rhe repeater cost may also be held low by utilizing pure time divisionfor multiplexing rather than frequency division. This results in a powersaving since a common output tube driven near overload may be usedinstead of many output tubes, that is instead of one for each channel,or instead of a common output tube operated ineciently.

= Pure time division in a broad-band system means that the pulseshandled will be very short if the number of chan.- nels is high. Thepresent repeater has therefore been designed to be capable of handlingextremely short pulses. For example a repeater as described in detailbelow is capable of handling binary pulses with a band width of overseveral hundred megacycles on the order of 9 millimicroseconds in lengthat a carrier frequency of 20,000 rnegacycles which permits the system tohandle 2,000 channels in time division. Time division also permitsflexbility in dropping channels. An important feature of the inventionis that the auxiliary amplifiers required need be only narrow banddevices.

in one embodiment only the main signal path requires broad-band devices.

With a repeater constructed in accordance with the present invention, itis economically feasible to space repeaters only a few miles apart;incomplete regeneration in each repeater will therefore be sufficient tomaintain a high quality system. If desired, completely regenerativerepeaters may be used in combination with several incompletelyregenerative devices to maintain the desired quality. l

These and other features and objects of the invention may be betterunderstood from a consideration of the following detailed descriptionwhen read in accordance with the attached drawings, in which:

Fig. 1 shows by a block schematic diagram an incompletely regenerativerepeater embodying principles of the present invention;

Fig. 2 shows schematically a repeater of the type shown in Fig. 1 i

Fig. 3 shows illustrative expander and limiter characteristics;

Fig. 4 shows wave forms illustrative of the circuits of Figs. 1 and 2;

Fig. 5 shows by a block schematic diagram another ernbodiment of theinvention;

Fig. 6 shows schematically a portion of the repeater shown in Fig. 5;and

Fig. 7 shows wave forms illustrative of the circuits of Figs. 5 and 6.

Referring now to Fig. 1 the signal comprising a train of microwavepulses is received by the receiving antenna 11 passed through a radiofrequency filter 12 and amplified by a broad band amplifier 13. Aportion of the amplifier 13 output is rectified by a crystal rectifier14 and the rectified output is applied to an automatic gain controlamplifier 15. The output of amplifier 15 acts on the amplifier 13 tohold the output of the latter constant.

Another portion of the output of amplifier 13 is applied to an expander16 followed by a limiter 17. The expander 16 increases the amplitude ofthe higher level signals relative to the amplitude of the lower levelsignals thus tending to separate the signals from the noise and thelimiter establishes a peak pulse amplitude. The output of the limiter 17is applied to a variable gain device 18 whose gain is varied at thepulse repetition rate. There is no component of the pulse rate frequencyin the envelope of the signal at the output of amplifier 13.

Therefore, a control wave having a frequency equal to the pulse rate isderived by rectifying aportion of the output of amplifier 13 by acrystal rectifier 19 and by passing the rectified signal through anarrow band amplifier 20 which is tuned to the nominal pulse rate. The

output of amplifier 20 is a sinusoidally varying voltage of the pulserepetition frequency.

The output of the variable gain device 18 is amplified by a broad-bandamplifier 21 and the band is narrowed by a filter 22 before the signalis transmitted by the transmitting antenna 23. Putting the filter 22ahead of amplifier 21 instead of after it may result in somewhat higheroutput but would permit radiation of the frequency components producedby any non-linearity in the amplifier 21.

Components to fill the blocks of Fig. 1. are shown by way of example inFig. 2. The incoming signal from the antenna 11 is passed through thefilter 12 which comprises a pair of spaced irises 26 and is then appliedto the input of traveling wave amplifier 27 by the wave guide 25.Traveling wave amplifiers are described in articles in the February 1947Proceedings of the I. R. E. entitled Traveling wave tubes by J. R.Pierce and L. M. Field, page 108, Theory of beam type traveling wavetubes by I. R. Pierce at page lll, and The traveling wave tube as anamplifier for microwaves by R. Kompfner at page 124. The traveling waveamplifier 27 comprises an indirectly heated cathode 29, a control grid30, an accelerating anode 31, a helix 32 and a collector 33. The helixis biased positive with respect to the cathode by the battery 34 and thecollector 33 is biased slightly less positive than the helix 32.

Output is taken from the traveling wave amplifier by wave guide 35 andapplied to a wave guide hybrid junction 36. Wave guide hybrid junctionsare disclosed, for example, in Patent 2,445,895 to W. A. Tyrrell, datedJuly 27, 1948. The p and s arms and the a and b arms of the hybrid arerespectively in a conjugate relation, that is, there is no directcoupling of energy between them so that energy entering the p arm Willdivide between the a and b arms, and will not couple directly into the sarm. The p or parallel arm is so-called because energy entering the parm and appearing in the a and b arms will have the same phase relationat equal distances from the junction in the a and b arms. The s orseries arm is so-called because energy entering the a and b arms fromthe s arm will have opposite phase relations at equal distances from thejunction. No especial use is made of the conjugate properties of hybridjunction 36, rather,` the' hybrid junction is used merely as aconvenient wave guide branching means.

Energy entering the b arm of hybrid junction 36 is rectified byrectifier 37 which may for example comprise a germanium crystalrectifier. A portion of the rectified output is applied to the input ofthe automatic gain control amplifier 15 by means of the voltage dividercomprising resistors 38 and 39. The output of amplifier 15 is applied tothe control grid 30 in the electron gun assembly of the traveling waveamplifier 27 in such a manner as to hold the output level of amplifier27 constant. The output of amplifier 15 might alternatively be appliedto the helix 32 of the traveling wave ampliner.

Energy entering the a arm of hybrid junction 36 is applied to thecrystal expander 16 which is of the type disclosed in a copendingapplication of C. C. Cutler Serial No. 118,890 filed September 30, 1949,which issued as Patent No. 2,652,541, dated September 15, 1953. Theexpander 16 comprises a hybrid junction similar toy the hybrid junction36 but with the a and b arms termf'-, nated in crystal rectifiers 40.The a and b arms are matched at low levels by the rectifiers 40 but asthe signal level increases, the impedance of the crystal diodes, changesand the a and b arms become progressively mismatched. Higher levelsignals will therefore be reflected into the s arm in increasing amountsas their amplitude increases. The b arm is a quarter wavelength longerthan the a arm so that energy reflected from the a and b arms will be inphase in the s arm and therefore add. An illustrative crystal expandercharacteristic is shown by way of illustrations by curve a of Fig. 3.lThe limiter 17 is similar in structure to the expander 16. However, therectifiers 41 which terminate the a and b arms of the limiter arematched at high levels so that the limiter has a characteristic asillustrated by curve b of Fig. Crystal diode limiters are disclosed in acopending application of A. F. Dietrich, Serial No. 118,856, filedSeptember 30, 1949, which issued September 15, 1953, as Patent No.2,652,540. The over-all characteristic of the expander 16 and limiter 17is illustrated by curve c of Fig. 3. It may be seen from the combinedcharacteristic that the expander-limiter combination will discrimif natein favor of the higher level signals, tending to sup-, press the lowerlevels, and will limit the higher levels to a value predetermined by thelimiter. The expander and limiter therefore constitute a slicer whichcontinually; samples a given amplitude range of the incoming signal; theexpander determining the lower limit of the range and the limiter theupper level. The shape of this char-4 acteristic may be adjusted byadjusting the levels at which, the crystals 40 and 41 of the expanderand limiter are matched to the respective wave-guide arms; this may. bedone, for example with the aid of a direct-current bias applied to thecrystals.

The output of the limiter 17 is applied by the wave guide 42 to thevariable gain device 18 which comprises. a traveling Wave amplifier 43similar to amplifier 27. The sinusoidally varying voltage which controlsthe gain of amplifier 43 is derived as explained above from the rectv-Ified pulse train which is amplified by the narrow band pass amplifier20. The sinusoidally varying voltage is' properly phased with respect tothe pulse train so that amplifier 43 will have maximum gain at thecenters of,

the normal pulse occurrence times as willV be illustrated below. Theoutput of the variable gain device 18 is passed through amplifier 21 anda filter 22 comprising the spaced irises 44 to the transmitting antenna23.

The variable gain device 18 may alternatively comprise a crystal diodestructure such as the expander 16 or limiter 17 with the sinusoidaloutput voltage of amplifier 22 being applied to the crystal rectifiersas a bias., Such a device is disclosed in the aforementioned,

Carbrey-Cutler-Feldman application.

an expander or limiter.

'not be broad band devices.

The siglial level atthe input of amplifier 43 Vis low due to thelossvxinthe expander 16 and limiter 17. Therefore, even if the variablegain device 18 is a crystal diode device it should, at this low level ofoperation, act as a switch rand not as It-may be noted that theamplifiers other than those in the main signal path, e; g. amplifiersand 20 need The repeater of Figi lis `therefore relatively simple,inexpensive and easy to build.

The `effect-of the repeater just described on an incomingtsignal isillustrated by the wave form shown in Fig. -4. The Vertical ylines 1, 2,3 10 indicate successive pulse lpositions and waveform a is 'a train ofvbinary pulses without noise. Wave form b illustrates what the additionof noise and/or fading may do to wave form a. After the signal haspassed through the expander and limiter the signaliwill appear as curvec. It 'may be Vseen that the 'higher level signals have been increasedand the lower level signals Vhave been decreased. Al-

though the amplitudes of the pulses have been pushed backtoward theircorrect values some of the pulses are slightly out of time. Thesinusoidal voltage which controls the variable gain device isillustrated as wave form d and the output of the variable gain device aswave 'better than the input signal, wave form b, both as to pulseamplitude and pulse position. If it were recirculated through therepeater without added noise the resulting output would be still morelike wave form a. However, the same effect may be had withoutrecirculation if there is substantially no noise or fading between thisand the next subsequent repeater. If a small amount of noise is added towave form f prior to the next repeater the output of the latter will beapproximately 'the same as wave form f.

An alternative embodiment of the invention is illustrated in Figs. 5 and6. Referring now to Fig. 5 microwave pulses received by antenna 51 areamplified by broad band amplifier 52. Gain control may be applied toamplifier 52, if desired, to assure that amplifier 52 delivers pulseswhich have a constant average amplitude. The amplified signal is thenpassed through a radio yfrequency slicer 53 and applied to the input ofa directional coupler 54. Most of the energy enteringthe a arm ofdirectional coupler 54 will be directly coupled to the .,b arm thereof,with a smaller portion being coupled to the d arm; the c arm of thecoupler is terminated in' its l characteristic impedance by an impedance55.

The energy appearing in the b arm of the directional coupler is appliedto the input of a gating tube 56 which is under the control of a sweepsource 57. The sweep source 57 drives the gating tube 56 at a frequencyequal to 4one-half the pulse repetition rate and is so phased that thegating tube will pass energy only at the center position of each pulseoccurrence time. Therefore, if a pulse arrives at the input of thegating tube, a short and accurately timed pulse appears at its output.vThispulse `is broadened to the desired thickness by filter 58 and is`amplified by amplifier 59. The amplified energy is applied todirectional coupler 60 which applies mo'st of the energy to amplifier 61and thence to the-transmitting antenna V62. It will be understood thatif-at a given `pulse occurrence time the slicer 53 delivers yno `pulseto the gating tube 56 no pulse will appear at the :output of `the gatingtube and hence no pulse will berradiated Aby the antenna. y

To insure'that the sweep source 57 isfaeeuratejy;.y chronized with theincoming pulses, the sweep Lsodi-"e 4frequency is controlled by acomparator circuitv 63 which 'compares a sample ofthe signal derivedfrom the outputofthe slicer 53 with a sample of the signal derivedj-from the 'output of amplifier 59. These samples are deriv'ec'lrbyvmeans of directional couplers 54 and 60 respectively. A delay line 64in interposed between directional coupler 54 and 4comparator circuit 63and lias v'a delay equal to the delay of gating tube 56, filter 58,

and amplifier 59 'and associated wave guide so that'the signals reachvthe comparator circuit 63 from 'the two directional couplers insynchronism It is important to `notethat'v'vhile large changes in thephase of the loutput of sweep'source 57 may cause completely falsesignals to appear at the output of gating tube 56 small changes in thephase of the sweep' source merely cause the pulses 'inthe output of thegating tube to appear at'a time slightly too early or too late.

"Details of an illustrative circuit constructed in accord- -a'nce withthe block schematic of Fig. 5 will be explained with reference to Fig.6. The radio frequency Slicer which is not shown may be of the typedisclosed in m'y copendingapplication,VSerial No. 225,468, filed May l0,'1951. Alternatively, it may comprise an expanderlimiter combination asdescribed above in connection with Fig. 2. In either case, it acts topass only those signals which originated as pulses and to suppresstho's'e induced by noise. The pulses appearing at the output of theSlicer 53 areapplied to the directional coupler `54 4which is of thetype disclosed in an article entitled Directional couplers by W. W.Mumford appearing in the Proceedings of the I. R. E., February 1947 atpp.

l'6'0*l65.' Theportion of the incoming 'signal to be apwave switches,controlling the signal derived fromslicer 53 by means of the d arm ofdirectional coupler 54 inra 'manner which will be explained.

The energy appearing in the d arm of directional cou- `pler 54 isapplied through a delay line 64 comprising a section of coaxial cable66, cut to the proper length, to

the p arm of a hybrid junction 67. Hybrid junction 67 divides the energyapplied to its p arm between the two previously mentioned microwaveswitches which comprise hybrid junctions 68 and 69. Hybrid junctions 68and 69 have their a and b arms terminated in crystal rectifiers 70-73which are spaced at equal distances from their respective junctions.Rectifiers 70 andA 71 `ordinarily present equal radiofrequencyimpedances to incident energy and preferably impedances whichmatch the characteristic impedance of their respective waveguide arm asdo rectifiers 72 and 73 so that there ordinarily is no signalltransferred through either hybrid junction 68 or 69. However, whenrectified output from crystal rectifier 65 is applied to rectifier 71over leads 74V and 75, the impedance of rectifier 71 is made differentfrom the impedance of rectifier 70. When these two -impedances areunbalanced, the hybrid will act as a closed switch, and energy will passfrom the p arm of .hybrid junction 68 to rectifier 76, the rectifiedoutput of :francas hybridjunction 69 to produce rectified output across.condenser 77.

' Between hybrid junctions 68 and 69 there is interposed a delay line 79comprising a section of coaxial conductor so that the pulses from hybridjunction 67 .reach hybrid junction 69 slightly out of phase with thepulses which reach hybrid junction 68. The result of this out-of-phaserelationship on the rectified outputs of rectifiers 76 and 78 may beunderstood by reference to Fig. 7; Wave form A illustrates the pulsesapplied to .rectifier 65 from the output of amplifier 59. When theamplitude of the signal in wave form A is maximum, the switches formedby hybrid junctions 68 and 69 are closed; when the amplitude is zero,these switches are opened. If the pulses arriving at hybrid junction 68Iare exactly in phase with the opening and closing of the switch, therectified output of rectifier 76 appearing across condenser 77 will beas illustrated by wave form B of Fig. 7, and the average voltage will beproportional to the shaded area. However, the pulses arriving at hybridjunction 69 will be delayed by an amount t, as illustrated by wave formC, due to the delay line 79 of Fig. 6. Therefore, these latter pulseswill not coincide with the closed periods of the switch 69, as shown inwave form A, and the average rectifiedout put voltage of rectifier 78appearing across condenser .77, which is represented by the shaded areaof wave form D, will be less than the rectied output area shown by theshaded area of B. Rectifiers 76 and 78 are con- .nected to produceopposite polarities across condenser 77. Therefore, as the phase of thepulses reaching directional coupler 54 varies with respect to the phaseof the pulses reaching directional coupler 60, the volt- Vage acrosscondenser 77 will change in magnitude and may change in polarity becauseof the phenomenon 'illustrated by wave forms B and D of Fig. 7. Aspreviously indicated, the phase of the pulses coming from gating tube 56is governed by the phase of the sweep voltage produced by sweep source57. Therefore, the

voltage across condenser 77, which is a measure of the phase of thesweep voltage as compared with the phase y'of the pulses coming fromslicer 53, may be used to control and stabilize the phase of the sweepsource, i. e., to synchronize the sweep source 57 properly with the.incoming pulses.

To do this, the voltage across condenser 77 is ampli- 'tied by adirect-current amplifier 81 whose output is 'balanced to ground byresistors 82. age 'is .used to control the frequency or phase of thesweep source 57 as follows.

This balanced voltvCoil :is coupled to a resonant circuit 92 which istuned to a frequency slightly above the desired sweep frequency whilecoil 91 is coupled to a resonant circuit 93 tuned to a frequencyslightly below the desired sweep frequency. The tuning of resonantcircuits 92 -and93 and the coupling of coils 90 and 91 to theirrespective resonant circuits are so adjusted that at the desired .sweepfrequency, the impedance looking into coil 90 from its connectingtransmission line 94 is resistive and is equal to the characteristicimpedance of trans mission. line 94. One side of resonant circuit 92 isconnectedto the control grid 95 of the pentode 96, the cathode 97 ofwhich is connected to ground through resistor-98 and by-pass condenser99. The anode 100 of pentode 96 is connected to one side of output coil101, the .other side of which is by-passed to ground by condenser' 102.The resonant circuit 93 is connected to Control grid 103 of a secondpentode 104 whose anode 105 is connected to the anode 100 of the firstpentode 96 and whose cathode 106 is connected to cathode 97 of pentode96.

Because of the off-tunings of the grid circuits of pentodes 96 and 104,pentode 96 is excited in a different phase from pentode 104. By changingthe polarity or magnitude of the control voltage applied to resonantcircuits 92 and 93 over leads 111 and 112, respectively, more currentmay be caused to flow through tube 96 and less through tube 104 or viceversa. Hence the components of the current supplied by the anodes and105 of the two pentodes to output coil 101 are controlled by thepolarity and the magnitude of the voltage appearing across resistors 82.

The combined output of the two pentodes 96 and 104 is coupled by coil101 into a resonant circuit 107 which is tuned to the desired sweepfrequency. One side of this resonant circuit is connected to the controlgrid 108 of the output tube 83, the other side being connected to groundby a by-pass condenser 109 and a grid leak resistor 110.

The foregoing description shows that the phase around the feedback pathfrom coil 89 to control grid 108 is controlled by the polarity andmagnitude of the balanced output of the direct-current amplifier 81appearing across resistors 82 and hence the frequency and phase of thevoltage produced across the output coil 88 and applied to the gatingtube 56 is controlled by the output of direct-current amplifier 81. Ifthis voltage is derived from the direct-current amplifier 81 in theright phase, the control action will be such as to maintain the sweepvoltage in the correct synchronization with the incoming pulses and toassure the proper operation of the overall repeater.

The gating tube comprises a traveling-wave amplifier 11,5 of the typedescribed above but having a deection coil 116 surrounding the helix117. The output of the sweep source 57 is applied to the deecting coil116 by means of the leads 118 and laterally defiects the electron beamof the tube. With zero deflection, the beam is centered longitudinallyin the helix and the tube will pass and amplify energy applied to itsinput by wave guide 119. However, a slight deflection of the beam willcause it to strike the helix and the tube will be, in effect, cut off.The sweep voltage is therefore initially phased with respect to incomingpulses to have zero deflection at the centers of each pulse position. Asan alternative device, the gating tube 56 may comprise a device such asis described in my copending application Serial No. 110,851, led August17, 1949.

Although the invention has been described with particular reference toillustrative embodiments other modifications and embodiments willreadily occur to one skilled in the art so that it should be understoodthat the invention' is not limited to the particular embodiments hereindescribed in detail.

What is claimed is:

l. A radio repeater for relaying radio frequency signals in the form ofsignal-modulated pulses which comprises means for receiving saidsignals, means for retransmitting said signals, and pulse regenerationmeans interconnecting said receiving and said retransmitting means, saidpulse regeneration means comprising amplitude discriminator means forpassing a fixed intermediate range of signal amplitudes and forsuppressing signals having amplitudes above or below said fixed range,an amplifier, means for varying the gain of said amplifier, means forderiving from said signals a voltage which varies sinusoidally at therepetition rate of said pulses, means .for applying said voltage to saidgain varying means to control the gain of said amplifier, and means forconnecting said amplitude discriminator means and 9 said amplifier inseries between said receiving means and said retransmitting means.

'2. A repeater for relaying and regenerating signals in the forml ofsignal-modulated pulses comprising means for receiving said signals,amplitude discriminator means comprising means Afor expanding anintermediate fixed range of signal amplitudes, means for applying saidreceived signalsto said amplitude discriminator means, amplifier means,means for applying the output of said amplitude discriminator means tothe input of said amplifier, means for varying'the gain of saidamplifier in an approximately sinusoidal manner, means for synchronizingsaid gain varying means with the average pulse repetition rate of saidsignals, and means for transmitting the output of said amplifier means.

3. The combination in accordance with claim 2 wherein said synchronizingmeans comprise means to cornpare the incoming pulse occurrence timeswith the outgoing pulse occurrence times, means to derive from saidcomparison a voltage which varies as the relative pulse occurrence timesvary, and means to apply said voltage to said amplifier to vary itsgain.

4. The combination of means for relaying microwave pulses whichcomprises means to receive said pulses, an expander, a limiter, avariable gain amplier, and means to retransmit said pulses all connectedin circuit, rectifying means, means to apply said pulses to saidrectifying means, a narrow band filter tuned to the nominal pulse rate,means to apply the rectified pulses to said filter, and means to applythe output of said lter to said variable gain amplifier to vary its gam.

5. Means for relaying radio frequency pulses which comprise means toreceive said pulses, means to retransmit said pulses, a circuitinterconnecting said receiving means and said retransmitting means whichincludes amplitude discriminator means the input-output characteristicof which includes an intermediate region of expansion, an amplifier, anda shaping filter, means comprising a rectifier and a narrow band filtertuned to the nominal pulse rate to derive from the received pulses avoltage varying at a frequency approximately equal to an integralmultiple of one-half of the repetition rate of said pulses and means toapply said voltage to said amplifier to vary the gain thereof in asinusoidal manner.

6. Means for relaying radio signals in the form of signal-modulatedpulses which comprise means to receive said signals, amplitudediscriminator means to pass signals lying within a predeterminedamplitude range in preference to all others, a variable gain amplifieremploying an electron beam, the gain of said amplifier being a functionof the trajectory of said electron beam, means to pass said receivedsignals through said amplitude discriminator means and said amplifier,means to derive from said received signals a voltage which varies in anapproximately sinusoidal manner at a frequency substantially equal to anintegral multiple of one-half of the incoming pulse repetition rate,means to apply said voltage to said amplifier to deflect said electronbeam, output means including a shaping filter and means to apply saidsignals to said output means after passing them through said amplitudediscriminator means and said amplifier.

7. Radio relay means for relaying microwave radio signals in the form ofsignal-modulated pulses which comprise means to receive said signals,amplitude discriminator means to pass the signals lying within apredetermined amplitude range in preference to all other, a variablegain amplifier employing an electron beam, the gain of said amplifierbeing a function of the trajectory of said beam, means to laterallydeect said electron beam in a recurrent manner at a rate approximatelyequal to an integral multiple of one-half of the normal incoming pulserepetition rate, means to synchronize said last-named means with theincoming pulses which comprises means to compare a sample of theincoming pulses with a sample of the pulses delivered by said amplifier,means to derive a voltage which varies in accordance with saidcomparison, and means to apply said voltage to said deflection means asa control therefor, output means including a filter and means connectingsaid amplitude discriminator means and said variable gain amplifier incircuit between said receiving means and said output means.

8. The combination in accordance with claim 7 wherein said amplifiercomprises a traveling wave amplifier.

9. Apparatus for regenerating radio signals in the form ofsignal-modulated pulses which comprises an input circuit, means to applysaid signal waves to said input circuit, an output circuit, amplitudediscriminator means including an expander and a limiter and variableimpedance means connected in circuit between said input and outputcircuit, means to vary said impedance which comprise a rectifier and anarrow band amplifier tuned to a frequency approximately equal to thenormal incoming pulse repetition rate connected in circuit, means toimpress a portion of the input signals on said lastnamed circuit, andmeans to impress the output of said amplier on said variable impedancewith the proper phase to cause said impedance to be a minimum during thenormal pulse occurrence times.

l0. The combination in accordance with claim 9 wherein said variableimpedance means comprises an amplifier.

ll. A microwave repeater for signals in the form of signal-modulatedpulses, said repeater having a main signal path including means toreceive incoming signals, means to amplify said signals, means toselectively pass the signals lying Within a predetermined amplituderange comprising an expander and a limiter, a variable impedance means,an output filter, and means to retransmit said signals, and an auxiliarycircuit to insure proper timing of said pulses which comprises means toderive from said incoming signals a substantially sinusoidal voltagehaving a frequency approximately equal to the normal pulse rate, andmeans to apply said voltage to said variable impedance means to varysaid impedance.

l2. A radio repeater for relaying and regenerating signals in the formof signal-modulated pulses comprising means for receiving said signals,amplitude discriminator means having a transmission characteristicincluding a range of expansion for higher amplitude input signals andranges of suppression for signals above and below said higher amplitudesignals, means for applying said received signals to the input of saidamplitude discriminator means, a traveling-Wave amplier having an input,an output, means providing a wave interaction path intermediate saidinput and output, and means for forming an electron beam which iiowsalong said path, means for applying the output of said amplitudediscriminator means to the input of said amplifier, means for modulatingsaid electron stream, means for deriving from said signal modulatedpulses a modulating voltage which has a frequency substantially equal tothe average repetition rate of said pulses, means for applying saidmodulating voltage to said modulating means, and means for transmittingthe output of said traveling-Wave amplifier.

13. The combination in accordance with claim l2 wherein said modulatingmeans comprises means for varying the density of said electron beam.

14. The combination in accordance with claim 12 wherein said modulatingmeans comprises means for laterally defiecting said electron beam.

15. A radio repeater for relaying radio frequency signals in the form ofsignal-modulated pulses which comprises means for receiving saidsignals, a slicer comprising amplitude discriminator means for passingsignals` within an intermediate amplitude range and for suppressingsignals above or below said range, means for apply- 11 ing said receivedsignals to said slicer, an amplifier having an input and an output,means for applying the output of said `Slicer to the input of saidamplifier, and means for varying the gain of said amplifier in anapproximately sinusoidal manner in synchronism with the averagerepetition rate of said signal-modulated puises.

References Cied inthe file of this patent UNITED STATES PATENTS -12-Hansell Aug. 12, 1947 Bailey Feb. 28, 1950 Labn et al. May v30, 1950Grieg et al. Oct. 10, 1950 Cutler Nov. 11, 1952 Feldman Feb. 3, 1953Mumford Mar. 30, 1954 FOREIGN PATENTS Great Britain Mar. 28, 1949

